We’re being asked to determine predict the sign of ΔH where the reaction is spontaneous and ΔS is positive
Recall that when ΔH and ΔS are given, we can determine the spontaneity of the reaction based on their signs.
We can use the Punnett square shown below:
Predict the sign of ΔS° for each of the following reactions. In addition, given the ΔH° values provided, predict at what temperatures (if any) the reactions would be spontaneous in the forward direction: low temperatures, high temperatures, or all temperatures. Circle your final answers.
2 NO2 (g) → 2 NO (g) + O2 (g), ΔH° = +113.1 kJ/mol
(Circle One) Sign of ΔS°: + -
Spontaneous at (Circle One):
i) Low temperatures
ii) High temperatures
iii) All temperatures
iv) Not spontaneous at any temperatures